1. Field of the Invention
The present invention relates in general to an automatic blood pressure measuring apparatus, and in particular to such an apparatus which provides blood pressure measurements or values with improved reliability.
2. Discussion of the Prior Art
There are generally known two types of automatic blood pressure measuring systems which automatically measure a blood pressure (BP) of a living body while pressing a limb or other body portion of the subject with a pressing device such as an inflatable cuff. The automatic BP measuring system of the K-sound type, as one of the two types, includes a sensor for detecting pulse sounds (Korotkoff sounds or "K sounds") produced from the pressed body portion of the subject as the pressing force of the pressing force is varied, and determines a BP value of the subject based on appearance and/or disappearance of the K sounds. The other known automatic BP measuring system of the oscillometric type is adapted to detect an oscillatory pressure wave (pulse wave) produced from the pressed body portion of the subject in synchronization with a noise-mixed pulsation of the heart (heartbeat) of the subject as the pressing force is varied, and determines a BP value of the subject based on variation in magnitude of the pulse wave.
However, the above K sound-type system suffers from a problem of detecting noises, such as sounds caused by rustling of clothes of the subject, mixed with the K sounds. Similarly, the above oscillometric-type system suffers from a problem of detecting noises, such as a pressure wave acting on the pressing device as a result of bending of the elbow or arm of the subject, mixed with the oscillatory pressure wave or pulse wave. The thus measured BP values are not sufficiently reliable, since those values are determined based on the K sounds and/or pulse wave detected with possibility of the noise mixture therewith. That is, the K sound-type system alone, or the oscillometric-type system alone is not sufficiently reliable.